1. Field of the Invention
The present invention relates to a gas conduit for a load lock chamber, and more particularly, to a gas conduit which can introduce gas into the load lock chamber with its maximum flow rate.
2. Description of the Related Art
Many semiconductor processes are conducted in vacuum, such as implantation and chemical vapor deposition (CVD). In order to maintain the vacuum in a reaction area, there must be a buffer area disposed in semiconductor equipment to switch the pressure therein from vacuum to 1 AMT. This buffer area is called the load lock chamber and accepts finished wafers from the reaction area or half-finished wafers delivered by a standard mechanical interface (SMIF).
FIG. 1 is a schematic drawing of semiconductor equipment with a conventional gas conduit. In FIG. 1, the SMIF 40 delivers the cassette 21 from the pod 20 to semiconductor equipment 10 or back to the pod 20. The SMIF 40 can open the pod 20, and place the cassette 21 on the support 41. Semiconductor equipment 10 has a load lock chamber 30 with two movable doors 34, 12, a buffer chamber 11 and a reaction chamber 14 and a robot arm 13. The doors 34 and 12 separate the load lock chamber 30 from the buffer chamber 11 and the SMIF 40. When the door 34 opens, cassette 21 are delivered from the SMIF 40 into the load lock chamber 30 and placed on the indexer 31. The door 34 closes, and an air-extracting device (not shown) pumps out the air and evacuates the load lock chamber. When the load lock chamber 30 reach base pressure. At the same time, the door 12 opens, and the robot arm 13 delivers half-finished wafers from cassette 21 into the reaction chamber 14 alternately to continue a predetermined process.
When all of the wafers in the load lock chamber 30 have finished the process. The load lock chamber 30 introduces gas to switch the pressure therein back to 1 atm., and then the door 34 opens so that the wafers in the cassette 21 are not damaged by the pressure change.
The inlet flow of the conventional load lock chamber 30 is controlled by a gas inlet assembly 33. The gas inlet assembly 33 includes a main pipe with a fast speed valve 333 and a bypass pipe with a limitative valve 332 and a low speed valve 331. When breaking vacuum in the load lock chamber 30, gas is introduced through the bypass pipe first. The flow speed is limited by limitative valve 332 until the pressure therein becomes larger than a predetermined pressure (ex: 200 Torr.). After the pressure increases, the bypass pipe is closed. At the same time, the fast speed valve 333 opens. The load lock chamber 30 continues introducing gas through the main pipe with the maximum flow rate of the fast speed valve 333 until the pressure becomes 1 atm.
Because the load lock chamber 30 does not introduce gas with its maximum flow rate at first, the gas introduction time increases. The average production time of each wafer is increased. Furthermore, the pipes are costly, and the control methods are more complicated.
Referring to FIG. 1 and FIG. 2, there is a filter 32 connected to the gas inlet assembly 33 and mounted on the bottom surface of the load lock chamber 30. The filter 32 is metal net with large holes which cannot filter out small particles. Furthermore, the air passing through the filter 32 mounted on the bottom surface of the load lock chamber 30 may easily disturb the particles deposited thereon, causing defects on wafers.